C4L 2019 AC works well on cold start as engine heats up reduces until compressor switches off and hottish air is felt

[Simonjs]

Despite strongly telling my car-dumb friend not to buy a French car in Brazil on finance....he went ahead and bought a Citroen C4 Lounge, a lovely car in many ways especially compared to the local third world 4 pot one litre death traps.

I let him park it in our private off street parking and he kindly lets me borrow it whenever I want during the week and in exchange I've been servicing the car and the biggest headache is the AC has never quite worked properly. Ever since an Air-Con tech unplugged the compressor to check the signal and plugged it back in again it has been working better than ever from a cold start but then almost randomly stops working at some point once the engine has got very hot.

1. Some type of bodge job repair was done where the evaporator temperature sensor was replaced with a fridge thermistor placed inside the engine bay and wired up directly to the compressor and the fridge thermistor sensor stuffed into the evaporator.

2. Stage 1 cooling fan kicks in around 97C though to me the engine bay and also the heater matrix inside the cabin seem absolutely scorching hot by the time the fan turns on. With AC on stage 1 fan comes on instantly. Stage 2 fan does seem to come on too but at this point I can barely touch the bonnet and bonnet stand without getting burnt.

3. Typically once the engine is extremely hot the compressor will at some stop functioning and the air blowing inside the cabin has some very hot air getting mixed in with the ambient temp air, though do bear in mind northeast Brazil is 29C at night where I am right now.


My obvious first concern is wondering why the fridge thermistor bodge job repair was done. I'm trying to locate the original evaporator temperature sensor to work my way back and see if I can replace it or discover some wiring loom issues in the hopes of putting it back as Citroen intended.

My other concerns are that the evaporator might be freezing causing the issues or one or more of the related pressure/temp sensors are faulty.

Where should I start from?

[PaulC5]

If the engine is getting to a high temperature then the air con is automatically switched off to reduce the load on the engine. I do not know at what temperature this is but if you use a code reader that gives live data then you can see at what engine temperature this happens.

[Simonjs]

If the engine is getting to a high temperature then the air con is automatically switched off to reduce the load on the engine. I do not know at what temperature this is but if you use a code reader that gives live data then you can see at what engine temperature this happens.

Thanks, my code reader only just arrived so I've only really used it parked up so far. Stage one seems to be kicking in on the fan at 97C as expected.

I'm going to replace the evaporator temperature sensor and undo the bodge job repair temporarily to see how it behaves. I'm a little concerned damage to the wiring loom may have been the reason behind the janky fridge thermostat fix as it seems just replacing the original temperature sensor is a lot less work the bodge job repair.